Ring Breathing Research Articles

FT-IR and FT-Raman characterization and investigation of reactive properties of N-(3-iodo-4-methylphenyl)pyrazine-2-carboxamide by molecular dynamics simulations and DFT calculations

The FT-IR and FT-Raman spectra of N-(3-iodo-4-methylphenyl)pyrazine-2-carboxamide were recorded and the experimentally observed wavenumbers are compared with the theoretically obtained wavenumbers. The redshift of the NH stretching mode in the IR spectrum from the computed value indicated the weakening of the NH bond. The ring breathing modes of the phenyl ring and pyrazine ring are assigned at 819 and 952 cm−1 theoretically. Using natural bond orbital analysis, the stability of the molecule arising from hyperconjugative interaction and charge delocalization has been analyzed. The most reactive sites in the molecule were identified by molecular electrostatic potential map. The calculations of the average local ionization energy (ALIE) were used for visualization and determination of molecule sites possibly prone to electrophilic attacks. Further information on possible reactive centers of title molecule has been obtained by calculations of Fukui functions. Vulnerability of title molecule towards autoxidation mechanism was investigated by calculations of bond dissociation energies (BDE), while vulnerability towards hydrolysis was investigated by calculations of radial distribution functions (RDF) as obtained after molecular dynamics (MD) simulations. Molecular docking studies suggest that the compound might exhibit inhibitory activity against mGluRs.

Surface Enhanced Hyper-Raman Scattering of the Amino Acids Tryptophan, Histidine, Phenylalanine, and Tyrosine

In this work, we report nonresonant surface-enhanced hyper-Raman (SEHRS) spectra of the amino acids tryptophan, histidine, phenylalanine, and tyrosine using silver nanoparticles. The spectra are obtained at an excitation wavelength of 1064 nm and compared to the corresponding surface-enhanced Raman scattering (SERS) spectra measured at 532 nm excitation. The majority of the bands in the SEHRS spectra are assigned. Important hallmarks of the spectra include strongly diminished or absent bands from the ring breathing modes. SEHRS and SERS spectra obtained from histidine and tyrosine indicate changes at slightly varied amino acid concentration. Small changes in the SEHRS spectra were more pronounced than variation in the corresponding SERS data, supporting the high sensitivity of the SEHRS spectra with respect to structural changes due to small variations in surface environment. The possibility to measure nonresonant SEHRS spectra of amino acids in solution and the complementary information obtained from the...

Resonance Raman and IR spectroscopy of aligned carbon nanotube arrays with extremely narrow diameters prepared with molecular catalysts on steel substrates.

Carbon nanotubes (CNTs) are considered promising for a large range of emerging technologies ranging from advanced electronics to utilization as nanoreactors. Here we report a controlled facile synthesis of aligned carbon nanotubes with very small dimensions directly grown on steel grid substrates via two-step catalytic chemical vapor deposition (CCVD) of a molecular catalyst (ferrocene) with ethylene as the carbon source. The system is characterized by resonance Raman spectroscopy and the results show single walled carbon nanotube (SWCNT) arrays composed of 0.80 nm to 1.24 nm semiconducting CNTs, as analyzed using Kataura analysis, which is approaching the lowest diameters attainable for SWCNTs. The G+ and G- mode splitting, G- line shapes and ring breathing modes (RBMs) are analyzed to characterize the CNTs. The approach results in close packed and vertically aligned SWCNT bundles formed into hair shapes, with some contribution from multiwall CNTs (MWCNTs). IR spectroscopy is utilized to characterize the edge/defect states that have the ability to form esters and ether bonds in the as-prepared CNTs. The stepwise deposition of the catalyst followed by the carbon source gives control over the formation of small diameter single walled carbon nanotubes (SWCNTs). The utilization of molecular catalysts for narrow diameter growth directly on steel grid substrates forms a promising approach for producing cost-effective CNT substrates for a plethora of sensing and catalytic applications.

Charge Transport, Mechanical and Storage Performances of Sepiolite Based Composite Polymer Electrolytes

AbstractIn the present report, electrochemical, thermal, mechanical and structural properties of the polymer electrolyte composed of Polyvinylidene fluoride (PVdF)‐Bis(trifluoromethane)sulfonimide (LiTFSI) for various concentrations of Sepiolite was investigated. Concentration of Sepiolite was optimised based on the ambient temperature conductivity. It was observed that 10 wt.% of sepiolite incorporated composite polymer electrolyte (CPE) showed a higher ionic conductivity in the order of 3.58 x 10−4 S cm−1. C−C stretching, C−F stretching and very strong ‐CF2 ring breathing vibrational modes of PVdF and the complexity of the prepared composite electrolyte were studied using FTIR and X‐ray diffraction analysis. The as‐prepared CPE is thermally stable up to ∼335 °C; the addition of sepiolite filler into the polymer salt matrix increased the storage modulus to 40 x 107 Pa from 12 x 107 Pa until 90 °C. The galvanic charge‐discharge performances of the CPE that exhibited high ionic conductivity were evaluated in the Li|PVdF‐LiTFSI‐Sepiolite|LiFePO4 half cell configuration. The cell showed a reversible capacity of 148 mAh g−1 in the second cycle; and exhibited capacity retention above 75 % even after 100 cycles. It was noted that the incorporation of eco‐friendly sepiolite into the polymer electrolyte greatly enhanced the thermal, mechanical, structural and electrochemical properties of the composite electrolytes.

Reactive Diazonium-Modified Silica Fillers for High-Performance Polymers.

We describe a simple way of modification of three silica-based fillers with in situ generated 4-hydroxymethylbenzenediazonium salt (+N2-C6H4-CH2OH). The rationale for using a hydroxyl-functionalized diazonium salt is that it provides surface-functionalized fillers that can react with phenolic resins. The modification of silica by diazonium salts was assessed using Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). FTIR spectroscopy permitted the tracking of benzene ring breathing and C-C. The absence of the characteristic N≡N stretching vibration in the 2200-2300 cm-1 range indicates the loss of the diazonium group. XPS results indicate a higher C/Si atomic ratio after the diazonium modification of fillers and the presence of π-π* C1s satellite peaks characteristic of the surface-tethered aromatic species. Adhesion of aryl layers to the silicas is excellent because they withstand harsh thermal and organic solvent treatments. Phenolic resins (used, for example, as binders in abrasive products) were filled with diazonium-modified silicas at 10-25 wt %. The reactivity of the fillers toward phenolic resins was evaluated by the determination of the flow distance. After annealing at 180 °C, the diazonium-modified silica/phenolic resin composites were mechanically tested using the three-point flexural method. The flexural strength was found to be up to 35% higher than that of the composites prepared without any diazonium salts. Diazonium-modified silica with surface-bound -CH2-OH groups is thus ideal reactive filler for phenolic resins. Such filler ensures interfacial chemical reactions with the matrix and imparts robust mechanical properties to the final composites. This specialty diazonium-modified silica will find potential application as fillers in the composites for the abrasive industry. More generally, aryl diazonium salts are a unique new series of compounds for tailoring the surface properties of fillers and tuning the physicochemical and mechanical properties of polymer composites.

Vibrational spectroscopic investigations, molecular dynamic simulations and molecular docking studies of N′-diphenylmethylidene-5-methyl-1H-pyrazole-3-carbohydrazide

FT-IR and FT-Raman spectra of N′-diphenylmethylidene-5-methyl-1H-pyrazole-3-carbohydrazide were recorded and analyzed. Due to the industrial and biological importance of pyrazole derivatives, we have carried out an extensive quantum chemical study on N′-diphenylmethylidene-5-methyl-1H-pyrazole-3-carbohydrazide. The theoretical ground state geometry and electronic structure of the title molecule were optimized by DFT/B3LYP/6-311G++(d,p) method and compared with those of the crystal data. The wave numbers obtained are assigned by potential energy distribution. The ring breathing modes of the benzene rings are assigned theoretically at 1009 cm−1 for the mono substituted phenyl rings. The first order hyperpolarizability is comparable with that of similar derivatives and 16 times that of the standard NLO material urea. Conformational analysis was conducted in order to locate all possible conformations of the title compound, followed by investigation of local reactivity properties by MEP and ALIE surfaces. Natural bond orbital analysis has been carried out to analyse the stability of the molecule arising from hyper-conjugative interactions and charge delocalization. Further, reactive properties via autoxidation and hydrolysis mechanisms have been assessed through calculations of bond dissociation energies and radial distribution functions. Docking results confirmed that the compound was a potential inhibitor of CDK2s and were in agreement with the previous reported studies.

Electrical and structural studies of a LiBOB-based gel polymer electrolyte

A series of gel polymer electrolytes (GPEs) containing lithium bis(oxalato)borate (LiBOB), propylene carbonate (PC), and ethylene carbonate (EC) have been investigated. Poly(ethylene oxide) (PEO) was used as the polymer. First, a series of liquid electrolytes was prepared by varying the Li:O ratio and obtained the best composition giving the highest conductivity of 7.1 × 10−3 S cm−1 at room temperature. Then, the PEO-based GPEs were prepared by adding different amounts of LiBOB and PEO into a mixture of equal weights of EC and PC (40 % of each from the total weight). The gel electrolyte comprises of 12.5 % of LiBOB, 7.5 % of PEO, 40 % of EC, and 40 % of PC gave the highest ionic conductivity of 5.8 × 10−3 S cm−1 at room temperature. From the DC polarization measurements, ionic nature of the gel electrolyte was confirmed. Fourier transform infrared (FTIR) spectra of electrolytes showed the Li+ ion coordination with EC and PC molecules. These interactions were exhibited in the peaks corresponding to ring breathing of EC at 893 cm−1 and ring bending of EC and symmetric ring deformation of PC at 712 and 716 cm−1 respectively. The presence of free Li+ ions and ion aggregates is evident in the peaks due to the symmetric stretching of O–B–O at 985 cm−1.

Label-free identification of antibiotic resistant isolates of living Escherichia coli: Pilot study.

We introduce a label-free spectroscopic method to classify subtypes of quinolone-nonsusceptible Escherichia coli (E. coli) isolates obtained from human blood cultures. Raman spectroscopy with a 30-nm gold-deposited, surface-enhanced Raman scattering (SERS) substrate was used to evaluate three multilocus sequencing typing (MLST)-predefined groups including E. coli ATCC25922, E. coli ST131:O75, and E. coli ST1193:O25b. Although there was a coffee-ring effect, the ring zone was selected at the ideal position to screen E. coli isolates. Strong Raman peaks were present at 1001-1004 cm-1 (CC aromatic ring breathing stretching vibrational mode of phenylalanine), 1447-1448 cm-1 (CH2 scissoring deformation vibrational mode), and 1667 cm-1 (amide I α-helix). Although the three MLST-predefined E. coli isolates had similar Raman spectral patterns, a support vector machine (SVM) learning algorithm-assisted principal component analysis (PCA) analysis had superior performance in detecting the presence of quinolone-nonsusceptible E. coli isolates as well as classifying similar microbes, such as quinolone-nonsusceptible E. coli ST131:O75 and E. coli ST1193:O25b isolates. Therefore, this label-free and nondestructive technique is likely to be useful for clinically diagnosing quinolone-nonsusceptible E. coli isolates with the MLST method.

Spectroscopic characterization of 1-[3-(1H-imidazol-1-yl)propyl]-3-phenylthiourea and assessment of reactive and optoelectronic properties employing DFT calculations and molecular dynamics simulations

IR and Raman spectra of 1-[3-(1H-imidazol-1-yl)propyl]-3-phenylthiourea (HIPPT) have been recorded in the solid phase and the vibrational wave numbers are calculated theoretically by B3LYP/6-31G(d,p) (6D, 7F) method. All the fundamental vibrational modes have been assigned using potential energy distribution values and the molecular structure was analyzed in terms of parameters like bond length, bond angles and dihedral angles. The ring breathing mode of the phenyl ring is observed at 1016 cm−1 in the IR spectrum, 1014 cm−1 in the Raman spectrum and at 1014 cm−1 theoretically. The values of polarizability and hyperpolarizabilities were calculated and nonlinear optical properties are discussed. The HOMO-LUMO plot reveals the charge transfer possibilities in the molecule. The NBO analysis was computed and possible transitions were correlated with the electronic transitions. In the title compound, the imidazole ring and CH2 groups are tilted from each other and the thiourea group is tilted from the phenyl ring. Using MEP plot the electrophilic and nucleophilic regions are identified. Local reactivity properties were investigated by analysis of ALIE surfaces and Fukui functions. Oxidation and degradation properties were initially assessed by calculation of bond dissociation energies of all single acyclic bonds. Determination of atoms with pronounced interactions with water molecules was performed by calculation of radial distribution functions after molecular dynamics simulations. Chargehopping rates were calculated within Marcus semi-empiric approach, employing both DFT calculations and MD simulations. The molecular docking computational predictions were complemented by the in vitro antibacterial activity evaluation.

Vibrational spectroscopic analysis, molecular dynamics simulations and molecular docking study of 5-nitro-2-phenoxymethyl benzimidazole

FT-IR and FT-Raman spectra of 5-nitro-2-phenoxymethylbenzimidazole were recorded and analyzed theoretically and experimentally. The splitting of NH stretching mode in the IR spectrum with a red shift from the calculated value indicates the weakening of the NH bond. The theoretical calculations give the phenyl ring breathing modes at 999 cm−1 for mono substituted benzene ring and at 1040 cm−1 for tri-substituted benzene ring. The theoretical NMR chemical shifts are in agreement with the experimental chemical shifts. The most reactive sites for electrophilic and nucleophilic attack are predicted from the MEP analysis. HOMO of π nature is delocalized over the entire molecule whereas the LUMO is located over the complete molecule except mono-substituted phenyl ring and oxygen atom. Reactive sites of the title molecule have been located with the help of ALIE surfaces and Fukui functions. In order to determine locations prone to autoxidation and locations interesting for starting of degradation, bond dissociation energies have been calculated for all single acyclic bonds. For the determination of atoms with pronounced interactions with water we have calculated radial distribution functions obtained after molecular dynamics simulations. The calculated first hyperpolarizability of the title compound is 58.03 times that of standard nonlinear optical material urea. The substrate binding site interactions of the title compound with Topo II enzyme is reported by using molecular docking study. Biological activity studies show that the title compound can be leaded for developing new anticancer agents.

Surface-assisted electron transfer reaction and stabilization of reduced state

The present study aims to probe the effect of silver nanoparticles (AgNPs) on the sorption behaviour of boroaluminosilicate glass (BASG). Firstly, BASG was loaded with AgNPs and benzotriazole (BT) and the glass exhibited surface-enhanced Raman spectrum of BT. The loaded BASG was equilibrated with copper (II) chloride solution and was investigated using ICP-AES, Raman spectroscopy, and luminescence measurements. It was observed that the glass matrix along with the sorbed copper ions showed luminescence, with a broad peak centered at ∼400nm, indicating the presence of copper ions in the Cu (I) state. However, in the absence of AgNPs, the glass matrix containing BT and sorbed copper ions failed to show luminescence implying that the copper ions are in the Cu (II) state. The glass matrix containing copper ions in addition to AgNPs and BT gave an enhanced Raman peak at 240 cm−1 (corresponding to Ag-Cl stretch with overlapping Ag-N stretch mode) and a shift of peak from 1022 (inplane trigonal ring breathing mode) to 1040 cm−1 and a broadening of the ring stretching modes at 1390 and 1575 cm−1. All these observations could be attributed to the interaction of copper ions with BT and the simultaneous uptake of chloride ions along with copper. The studies suggest that both AgNPs and copper ions bind to the nitrogen atoms of BT and form a nanoarray like assembly AgNPs-BT-Cu which facilitates the diffusion/tunnelling of electrons from AgNPs to Cu (II) ions resulting in the reduction of Cu (II) to Cu (I).

Synthesis and Evaluation of Heat-Resistant Silver-Platinum Alloy Nanoprisms for Application in Cancer Therapy and Imaging

Nano-sized metal particles have been received great attention in the field of bioimaging and therapy, i.e. cancer treatment, because of their unique optical properties resulting from localized surface plasmon resonance (LSPR). Multifunctional nanoparticles have been developed for the precisive diagnosis and noninvasive cancer therapy in place of traditional surgery and chemotherapy, which can be restricted by region, physical strength, and so on. While various metal nanoparticles have been explored, the use of those consisting of Ag has been limited because of their physical instability. In particular, Ag nanoprisms (AgPRs) can be easily degraded by thermal energy generated along with the LSPR excitation because of their high surface energy. However, use of the AgPRs will provide a sufficient possibility for precisive cancer diagnosis due to the generation of significantly-enhanced electromagnetic fields. In this study, we developed AgPRs-based Pt-Ag alloyed nanomaterials (AgPtPRs), which can act as multifunctional therapeutic/diagnostic agents with improved thermal stability and bioimaging capability. The Ag nanoprisms (AgPRs) exhibiting a peak within near-infrared (NIR) wavelengths were synthesized according to the method reported by Mirkin.1) The formation of the AgPRs with an average edge length of 40 nm and thickness of 8nm were confirmed by TEM images. The AgPtPRs were synthesized by galvanic replacement of the as-prepared AgPRs with hexachloroplatinic (IV) acid. After the reaction, while the size as well as the morphology of them were almost maintained, the plasmon extinction peak slightly red-shifted. This result implies that thin Pt layers formed over the AgPRs surfaces. Thermal-durability evaluated by the irradiation of a continuous laser (2 W, 808 nm) for 1 h and heating in waterbath at 95 °C for 1 h. The morphology of the non-alloyed AgPRs were easily degraded by both of the laser irradiation and the exterior heating because of their high vertices energy. The optical properties of the AgPRs were destroyed by the deformation. In contrast, thermal-durability of the AgPtPRs against both of them was appreciably improved by the alloying reaction with Pt atoms. The photothermal conversion efficiency (PCE) obtained by the irradiation of NIR laser (808 nm, 2 W) were calculated to be ca. 65% even after the alloying reaction. The value was quite higher than those of the previous-reported major photothermal nanoparticles, e.g. Au nanorods (22 %) and Au nanoshells (13 %).2) In order to search the source of the higher PCE, the scattering and absorption components consisting of the extinction were calculated using a simulation of boundary element method (BEM). The absorption of the AgPRs modeled as the triangular structures with edge length of 40 nm and the thickness of 8 nm was dominant in the extinction peak. The optical tendency was almost maintained even after covering the AgPRs with Pt thin shells with 0.4 nm in thickness. The factor of large PCE of AgPtPRs and AgPRs was considered to be due to the high absorption coefficient. Next, we evaluated the effect of the photothermal phenomenon of AgPtPRs on the cancer cells. After the Hela cells were incubated with various concentrations of AgPtPRs modified with folic acid-conjugated polyethyleneimine, the cells were washed with phosphate buffered saline (PBS) several times. While the irradiation of the laser with 808 nm (2W) to the cells incubated with the AgPtPRs led to the efficient death of cells, non-incubated cells was not affected by the irradiation. The cell viability with and without the laser irradiation was ca. 12.9 % and 87.3 %, respectively. It was found from these results that the AgPtPRs have sufficient ability as a photothermal therapy nanomaterial with a high biocompatibility. In order to evaluate the imaging ability, surface-enhanced Raman scattering (SERS) properties of 4-mercaptobenzonic acid (4-MBA) immobilized on the nanoprisms were measured with a NIR laser of 785 nm. Those on the AgPRs and AgPtPRs showed Raman peaks characteristic of 4-MBA at 1590 cm-1 (C-C stretching) and 1080 cm-1(ring breathing). These results demonstrated that the strong local fields generated even after covering with the Pt shell led to the enhancement of the Raman signals for the SERS-imaging technique. 1). G. S. Métraux et al., Adv. Mater., 2005, 17, 412. 2). C. M. Hessel et al., Nano Lett., 2011, 11, 2560. Figure 1

Vibrational and structural properties of barbiturate anions in supramolecular compounds

In this work we have been successful in the synthesis, spectroscopic and structural characterization of five new supramolecular compounds of formulation [Ni(4dbpy2)2(H2O)2]Bb2·4H2O (1), [Mn(4dbpy2)2(H2O)2]Bb2·4H2O (2), [Mn(5dbpy2)2ClH2O][(C4O3N2H2)2-OH]·H2O (3), [Co(5dbpy2) (H2O)4]Bb2·2H2O (4) and [6dbpy2H] [(C4O3N2H2)2-OH]·H2O (5) which have been obtained from barbituric acid (HB) and 2,2′-bipyridine (4,4′, 5,5′ and 6,6′-dimethyl) building block ligands and transition metal ions, where Bb is the barbiturate monoanion and dbpy is the neutral substituted bipyridyl in the formulation. Compounds 1 and 2 are isomorphous, presenting the cationic block [M(4dbpy2)2(H2O)2]2+ neutralized by two uncoordinated barbiturate anions, whilst for compound 4 the different cationic units [Co(5dbpy2) (H2O)4]2+ are neutralized by the same anion. For the compounds 3 and 5 the formation of a new building block is recognized and characterized as the hydroxyhydurilate anion which has been generated in situ from the oxidation reaction between alloxan and the barbiturate anion. The Raman spectral analysis clearly shows the similarity of compounds 1 and 2 through similar wavenumber positions of all the vibrational bands, especially the band at 679cm−1 assigned to the ring breathing mode of the barbiturate anion which is present in compounds 1, 2 and 4. For compounds 3 and 5 the absence of this Raman band suggests that a noteworthy chemical modification has taken place in this building block and the appearance of a new band at 1745cm−1, assigned to the ν(CO) mode of the new hydroxyhydurilate anion generated in situ, supports this conclusion.

Surface enhanced Raman scattering of single 1,4-Benzenedithiol molecular junction

Here, we present simultaneous electronic and optical measurements of a single 1,4-benzenedithiol (BDT) molecular junctions to investigate the electronic and structural details in the molecular junction and to understand the charge transport property at the single molecular scale. The electronic property was investigated by DC conductance measurement while structural property was characterized using surface enhanced Raman scattering (SERS) measurement. The single BDT junctions sandwiched between Au nanogap-electrodes were prepared by the mechanically controllable break junction method at ambient conditions. The simultaneous conductance and SERS measurements demonstrate that ring deformation mode coupled to C–S stretching mode, ring breathing mode, and C=C stretching mode are detectable for the single BDT molecular junctions with electronic conductance of [Formula: see text] [Formula: see text]. The single molecule origin is supported by the characteristic variability of SERS within samples. Time evolution of the conductance and SERS signals indicated that the molecular conductance and the vibrational energy of the ring breathing mode exhibits anti-correlated relationship. This relationship can be mediated by time evolution of structural change in the single molecular junction and corresponding change in strength of metal–molecular coupling. The larger metal–molecular coupling causes higher electronic conductance of the molecular junction while charge transfer effect leads to weakening of molecular bonds and thus a resulting decrease in the vibration energy of the ring breathing mode.

Shell-isolated nanoparticle-enhanced Raman spectroscopy study of the adsorption behaviour of DNA bases on Au(111) electrode surfaces.

For the first time, we used the electrochemical shell-isolated nanoparticle-enhanced Raman spectroscopy (EC-SHINERS) technique to in situ characterize the adsorption behaviour of four DNA bases (adenine, guanine, thymine, and cytosine) on atomically flat Au(111) electrode surfaces. The spectroscopic results of the various molecules reveal similar features, such as the adsorption-induced reconstruction of the Au(111) surface and the drastic Raman intensity reduction of the ring breathing modes after the lifting reconstruction. As a preliminary study of the photo-induced charge transfer (PICT) mechanism, the in situ spectroscopic results obtained on single crystal surfaces are excellently illustrated with electrochemical data.

High‐throughput screening of measuring conditions for an optimized SERS detection

Surface‐enhanced Raman spectroscopy (SERS) is a perfect method for analytical applications because of delivering specific molecular information combined with a high sensitivity when applying rational design metallic nanostructures. However, the pH level and the activation of ctheir mutual influence. Besidesolloidal SERS substrates influence the sensitivity and comparability of the SERS analysis. In this study, a routine is presented that allows for a fast and effective recognition of the influences of pH and activating agents on the SERS signal of an analyte molecule. To do so, a citrate‐reduced Ag colloid served as SERS substrate. The influence of four activating agents as well as five pH levels on the SERS signal of the model analyte melamine was investigated. Here, not only the influence of the anion but also that of the cation of the activating agents was examined. In addition to different signal intensities, a shift of the dominant melamine signal occurred depending on the adjusted conditions. At pH 11, the lowest intensities of the SERS signal from the model analyte melamine were detected. The maximal enhancement of the ring breathing II mode in combination with this specific colloid was achieved using sodium chloride as an activating agent at a pH level of 5. Thus, the study introduces a routine, which can be applied on various analyte molecules to optimize the SERS intensity by changing the activation agent as well as the pH. Copyright © 2015 John Wiley & Sons, Ltd.

Discrimination of Fluoroamphetamine Regioisomers by Raman Spectroscopy

AbstractThe ability of a portable Raman spectrometer to perform on‐site and real time discrimination of fluoroamphetamine regioisomers demonstrated in this study. It suggests the presence and the position shifts of Star of David ring breathing vibration around 1000 cm−1 and CF stretching vibrations are assigned at 1232 cm−1 (2‐FA), 1241 cm−1 (3‐FA) and 1217 cm−1 (4‐FA) are good indicators to differentiate ortho‐, meta‐ and para‐FAs, whereas the CF vibrational shifts can help to confirm the determination.

The geometrical change and intramolecular energy transfer upon S1←S0 excitation in cyclopentanone.

The ultrafast dynamics in vibrationally hot S1 electronic excited state in cyclopentanone molecule was discovered with time resolved spectroscopy. Investigation of the geometry change upon the S1←S0 excitation and D0←S1 ionization has shown that the dihedral angle between the C=O bond and the plane given by the carbonyl and the α-carbons is 180° either in S0 or D0 state and is reduced to 145.8° by out-out-plane deformation of the oxygen in S1 state according to the theoretical calculation. The time domain experiments with femtosecond resolution have given rich insights into the energy transfer of the cyclopentanone molecule. The molecules are excited to the vibrationally hot S1 (n, π(∗)) state following absorption of one 267-nm photon. It is found that the population of the S1 (n, π(∗)) state undergoes ultrafast internal conversion to the highly vibrationally hot S0 state within 80 fs and nonradiative deactivation by intersystem crossing to triplet T1 (n, π(*)) state occurring in 3.14 ps. Several Rydberg states have worked as stepping stones during the ionization. The available energy was distributed in the symmetric methylene group wagging and the symmetric skeletal ring breathing modes in D0 state.

Direct visual evidence of end-on adsorption geometry of pyridine on silver surface investigated by surface enhanced Raman scattering and density functional theory calculations

Fourier transform Raman (FT-Raman) spectra of neat pyridine (Py) and surface enhanced Raman scattering (SERS) spectra of Py with silver nanoparticles (AgNPs) solution at different molar concentrations (X=1.5M, 1.0M, 0.50M, 0.25M, and 0.125M) were recorded using 1064nm excitation wavelength. The intensity of Raman bands at ∼1003 (ν11) and ∼1035 (ν21) cm−1 of Py is enhanced in the SERS spectra. Two new Raman bands were observed at ∼1009 (ν12) and ∼1038 (ν22) cm−1 in the SERS spectra. These bands correspond to the ring breathing vibrations of Py molecules adsorbed at the AgNPs surface. The value of intensity ratios (I12/I11) and (I21/I22) is increased with dilution and attains a maximum value at X=0.5M and upon further dilution (0.25 and 0.125M) it drops gradually. The theoretically calculated Raman spectra were found to be in good agreement with experimentally observed Raman spectra. Both, experimental and theoretical investigations have confirmed that the Py interacts with AgNPs via the end-on geometry.

Surface enhanced Raman spectroscopic (SERS) behavior of substituted propenoic acids used in heterogeneous catalytic asymmetric hydrogenation

The strength and geometry of adsorption of substituted propenoic acids on silver surface were studied by means of surface enhanced Raman spectroscopy (SERS) using silver sol. Based on their SERS behavior, two classes of phenylpropenoic acids studied were distinguished. The first class of propenoic acids (atropic acid, (E)‐2,3‐diphenylpropenoic acid, (E)‐2‐(2‐methoxyphenyl)‐3‐phenylpropenoic acid, (E)‐2,3‐di‐(4‐methoxyphenyl)phenylpropenoic acid and (E)‐2‐(2‐methoxyphenyl)‐3‐(4‐fluorophenyl)propenoic acid) has shown strong charge transfer (CT) effect. We suggest bidentate carboxyl bonded species based on the SERS enhanced bands of νCOO− around 1394 cm−1 and νC―C of the ―C―COO− moiety at 951 cm−1. In these series the plane of the α‐phenyl group (γCH out‐of‐plane vibrations at 850–700 cm−1) is almost parallel to the silver surface, while the β‐phenyl group is in tilted position depending on the type and the position of substituent(s) showing strong SERS enhanced bands of νCC + βCH (in‐plane mode) at 1075 cm−1, νCC (ring breathing mode, in‐plane) at 1000 cm−1 and γCCC (out‐of‐plane mode) around 401 cm−1. The other class of propenoic acids (cinnamic acid, (E)‐2‐phenyl‐3‐(4‐methoxyphenyl)propenoic acid) has shown weak electromagnetic (EM) enhancement (CC bands is enhanced in cinnamic acid). In this case no significant carboxyl enhancement was observed, so we suggest that adsorbed species lie parallel to the surface. The two types of adsorption can be related to the dissociation ability of the carboxylic group. In the first case the carboxylic H dissociates, while in the second case it does not, as indicated also by the characteristic νCO band at 1686 cm−1 in the FT‐Raman spectra of methanolic solutions. Copyright © 2015 John Wiley & Sons, Ltd.